Finally, regarding generalizability of the findings from this exclusively lean study sample, since postprandial FGF21 responses to sugars have been shown to be elevated in individuals with obesity (14), but human FGF21 responses to low protein diets have not been specifically studied in obesity, it remains uncertain how sugar and protein would interact in the setting of obesity. This evidence concerns the gene FGF21 and obesity due to melanocortin 4 receptor deficiency.